1. Field of the Invention
The present invention relates to a refrigerator, and more particularly to a refrigerator which can effectively remove a frost formed at an outer surface of an evaporator by using a wasted heat generated from a compressor.
2. Description of the Prior Art
Generally, a refrigerator is a device for storing foodstuffs at a relatively low temperature in order to maintain a freshness of the foodstuff. The refrigerator comprises a compressor, a condenser, an expansion valve and an evaporator. It is common knowledge that a working fluid called as a refrigerant circulates through a thermodynamic cycle. In such systems, a low pressure refrigerant is compressed by the compressor and leaves the compressor as a vapor at an elevated pressure, and then condenses in the condenser, resulting in a transfer of a heat to an environment surrounding the condenser. High pressure liquid refrigerant then passes through the expansion valve in which some of the liquid refrigerant flashes into vapor. The remaining refrigerant is vaporized in the low pressure evaporator, resulting in a transfer of a heat to the evaporating refrigerant from the environment, thereby cooling a surrounding air. The chilled air generated at a periphery of the evaporator is blown into a freezer compartment by a fan. The refrigerant vapor is then drawn into the compressor, and the cycle begins again. In short, in the evaporator, the refrigerant absorbs a heat from the surroundings and, in the condenser, it gives a heat off.
During the cooling cycle, ice builds up on an outer surface of the evaporator because the temperature of an outer wall of the evaporator is substantially below the freezing point of water. Accumulated ice may act as an insulator and provide a thermal barrier which interferes with the heat transfer between the refrigerant in the evaporator and the outside environment. This in turn results in a significant decrease in the efficiency of the refrigerator. Accordingly, the compressor has to work harder and longer to provide the required thermodynamic cycle. Also, further energy is required to melt the ice.
Generally, automatic defrosting refrigerators use a heat from an external source to melt the ice. Typically, a resistive heating element is connected to the evaporator or mounted in a position adjacent thereto. Then, in response to a timer, electric current is passed through the element during an off cycle of the compressor.
FIG. 1 shows a conventional refrigerator 100 having a heater 170.
As shown in FIG. 1, refrigerator 100 comprises a cabinet 110. Cabinet 110 is formed therein with a refrigerating compartment 130 for receiving foodstuffs which are to be maintained fresh at a relatively low temperature and a freezer compartment 120 for receiving foodstuffs which are to be maintained in a frozen state. Freezer compartment 120 is formed at a rear portion thereof with a space section 140, in which an evaporator 160 for generating a chilled air is installed. Refrigerating and freezer compartment 130 and 120 are divided by a wall section 152, and freezer compartment 120 and space section 140 are divided by a wall section 150.
A compressor(not shown) is installed below refrigerating compartment 130 for compressing and circulating the refrigerant. Vapor-phase refrigerant with high pressure and high temperature which has passed through the compressor gives a heat to a surroundings in the condenser(not shown), and is condensed into liquid phase. The liquid-phase refrigerant then passes through the expansion valve(not shown) in which some of the liquid-phase refrigerant flashes into vapor. The remaining refrigerant is vaporized in the low pressure evaporator 160 installed in a predetermined position in space section 140, resulting in a transfer of heat to the evaporating refrigerant from the environment, thereby cooling a surrounding air.
Wall section 150 is formed at an upper portion thereof with an opening 155 for introducing the chilled air generated by the evaporator into freezer compartment 120. A fan 180 driven by a motor 185 is installed in space section 140 at a position corresponding to a position of opening 155 for smoothly blowing a portion of the chilled air generated at a periphery of evaporator 160 into freezer compartment 120. The rest of the chilled air flows into refrigerating compartment 130 through a passage 145 formed in a rear wall of cabinet 110.
The chilled air flown into the refrigerating and freezer compartment 130 and 120 absorbs a heat from stored foodstuffs and returns to space section 140 through return passages 135 and 125 formed at wall section 152 so as to be cooled again in the above-described manner.
Meanwhile, a heater 170 is provided adjacent to evaporator 160 for removing a frost formed at an outer surface of evaporator 160, and is operated while a defrost operation is being carried out.
Heater 170 melts the ice by using a radiant heat radiated therefrom, and at this time, the temperature of an outer wall of heater 170 rises to an order of, for example, 400 degrees in Celsius. To prevent the radiant heat, radiated from heater 170, from being transferred into freezer compartment 120, wall section 150 is made of an insulator.
However, in the conventional refrigerator having heater 170, only a part of a power is consumed by heater 170 for defrosting, and the rest of the power is radiated into freezer compartment 120. The rest of the power is radiated into freezer compartment 120 through opening 155 formed at wall section 150, thereby raising the temperature of freezer compartment 120. To compensate for the rise in temperature of freezer compartment 120, a conventional refrigerator drops the temperature of freezer compartment 120 to 20 degrees below zero before carrying out the defrost operation, so an efficiency of a refrigeration is decreased and a power consumption is increased.
Meanwhile, U.S. Pat. No. 4,420,943 issued to Lawrence G. Clawson on Dec. 20, 1983 employs a thermal mass which is located in parallel with a condenser and receives a compressed refrigerant from a compressor. The compressed refrigerant transfers a heat to the thermal mass which stores the heat for a subsequent defrost operation. During the defrost operation, the compressor is deactivated and a solenoid valve is opened to fluidly connect the thermal mass to the outlet of the evaporator in bypass of the compressor. With this bypass valve opened, the pressure of the evaporator and the condenser equalize to an intermediate pressure. The refrigerant in contact with the thermal mass boils at the reduced pressure, thereby drawing a heat from the thermal mass. The vaporized refrigerant flows through the bypass valve to the evaporator and condenses in the relatively cool environment, thereby giving off heat to the evaporator, which melts the ice on an outer surface of the evaporator. However, the pressure equalization results in an undesirable heat transfer from the surroundings to the condenser. Moreover, because the thermal mass is located in parallel with the condenser, it does not in any way facilitate a cooling of the liquid refrigerant being circulated through the system during the normal thermodynamic cycle taking place while the compressor is operating, and thus does not increase the overall efficiency of the refrigerator during a normal operation.